The apparatus used in present day power generation systems typically require a high pressure coal supply system. In particular, many of these high pressure systems include high pressure reactors which combust the coal to produce heat or to further refine the carbon from the coal. The high pressure is used to nearly instantaneously combust the coal to produce the desired energy release. Coal, even when highly pulverized, is substantially a solid material and difficult to pressurize to the high pressures needed for combustion. To assist in providing the coal and achieving the high pressures required for combustion thereof, the coal is often formed into a slurry. The slurry then can be more easily pumped and pressurized to the required high pressures. Generally, it is desired to have the coal pressurized to at least 1000 psig.
Various systems have been developed to provide the high pressure coal required, but these systems all have numerous inefficiencies. With such systems, coal is generally first placed into a slurry of some form. The slurry includes a liquid, such as water, with the coal particles suspended therein. The carrier fluid of the slurry is also provided to the reactor as a large surplus in the slurry, thereby decreasing the efficiency of the reactor.
One specific, previously developed system is a lock hopper feeder system. With this type of system, the hoppers are first pressurized and then emptied into the pressurized system. After the first hopper is emptied the system is closed, then a second hopper is pressurized, and then emptied into the pressurized system. This system provides only a substantially discontinuous feed of the pressurized coal.
Other systems have been proposed which produce a liquid carbon dioxide and coal slurring which is then fed into the combustion or reaction system. Nevertheless, these systems still require the unreliable cycling lock hoppers to initially increase the pressure of the slurry. Moreover, the cycling lock hoppers generally include multiple valves and gas compressors that are inefficient and require nearly constant maintenance.
Still other systems have attempted to provide a feeder system which uses a screw feeder or pump, but has similar disadvantages. In particular, they generally require a plurality of heat exchangers around the feeder itself to provide the proper temperature of the carbon dioxide (CO2) that is fed into the coal in the feeder. These rely upon the solidification of the liquid CO2 pumped into the feeder to provide a seal to stop the backflow of the material as it goes from the low pressure input to the high pressure output. These systems do not easily overcome the high pressure head against which the coal is pumped.
Therefore, it is desired to provide a system that will allow for a continuous feed of coal into a high pressure coal system for gasification and other high pressure systems. In particular, it is desired to provide a continuous coal feed system which can use relatively inexpensive CO2 gas for delivering the coal to the combustor at ambient temperature at its static bed bulk density. Also, it is desired to provide a system that can provide the high pressure coal slurring through no more than two holding tanks, to thereby provide a high pressure supply tank for the high pressure reactors.